Wireless receiver apparatus and method

ABSTRACT

Embodiments of the invention include a wakeup receiver (WRX) featuring a charge-domain analog front end (AFE) with parallel radio frequency (RF) rectifier, charge-transfer summation amplifier (CTSA), and successive approximation analog-to-digital converter (SAR ADC) stages. The WRX operates at very low power and exhibits above-average sensitivity, random pulsed interferer rejections, and yield over process.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims priority from U.S. Provisional PatentApplication No. 62/897,770, filed Sep. 9, 2019, which is incorporated byreference in its entirety herein.

FIELD OF THE INVENTION

The invention is in the field of low-power sensor networks such as thosethat facilitate the internet of things (IoT).

BACKGROUND

Networks of wireless sensor nodes have become ubiquitous in the internetof things (IoT). As the technologies related to IoT evolve, the maingoals for development of components include improved (reduced) powerconsumption, increased speed/higher data rate, better sensitivity, androbustness.

Ultra low power (ULP) receivers are gaining traction in various consumerand industrial markets as new standards are being defined to supportthem in IoT devices. Communication standards such as WiFi 802.11ba, BLE,and NB-IoT are all considering operating modes and signaling that takeadvantage of ULP receivers as companion radios for several reasons. Theysignificantly reduce active and average power while providing continuousconnectivity, thus enabling batteryless operation. They also simplifyprovisioning of new nodes, reduce synchronization energy overhead andlatency to nearly zero, scale to networks of 1000s of nodes, and enablemicrosecond (ms) wakeup latency. ULP receivers have been demonstratedwith better than −100 dBm sensitivity and 10 nW, but none have addressedaspects for widespread adoption such as selectivity, random pulsedinterferer rejection, yield over process, voltage and temperature (PVT)variations, and security against replay or energy attacks.

A key component of wireless sensor networks are sensor nodes, whichinclude main circuit components such as wakeup receivers (WRXs). Becauseof the nature of the network, these receivers are typically ULPreceivers. Most IoT networks comprise many ULP receivers that are taskedwith receiving radio frequency (RF) wireless signals over the air (OTA)and taking some local action based on the ULP receiver's interpretationof the received RF signals. Translating the received RF signal into alocal action typically involves translating the continuous RF signal tosome discrete “on/off” (e.g., Wakeup) type of message to a localcomponent of the IoT system.

Current sensor nodes may have some low power characteristics. Forexample, certain ULP receive frontends that feature continuous-timeanalog circuitry do consume a relatively low amount of power. But theyexhibit low sensitivity, and poor robustness in the presence ofinterference and across wide temperature range .

Another current type of ULP receive frontend is an intermediatefrequency (IF) frontend with a continuous-time mixer and amplifiers.This type of frontend exhibits good sensitivity and selectivitycharacteristics, but consumes a relatively large amount of power.

Current ULP receiver frontends tend to rely on continuous-time analogapproaches to receive, process, translate, and transmit RF signals insensor networks.

It would be desirable to have a ULP receiver that overcomes the statedchallenges of the current solutions. It would be desirable to have a ULPreceiver that operates at very low power, and exhibits: above-averagesensitivity; random pulsed interferer rejections; yield over process;voltage and temperature (PVT) variations; and security against replay orenergy attacks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a die including circuit components of a ULPreceiver according to an embodiment.

FIG. 1A is an illustration of a sensor node, according to an embodiment.

FIG. 2 is a system block diagram of a sensor node, according to anembodiment.

FIG. 3 is a block diagram of a wakeup receiver (WRX) circuit, accordingto an embodiment.

FIG. 4A is a diagram of a parallel radio frequency (RF) rectificationcircuit, according to an embodiment.

FIG. 4B is a diagram of a charge-transfer summation amplification (CTSA)circuit, according to an embodiment.

FIG. 4C is a diagram of a successive approximation analog-to-digital(SAR ADC) circuit, according to an embodiment.

FIG. 5 is block diagram showing clock generation circuit inputs andoutputs, according to an embodiment.

FIG. 6 is a series of signal timing diagrams illustrating ULP receiveroperation, according to an embodiment.

DETAILED DESCRIPTION

Embodiments of the invention include a wakeup receiver (WRX) featuring acharge-domain analog front end (AFE) with parallel radio frequency (RF)rectifier, charge-transfer summation amplifier (CTSA), and successiveapproximation analog-to-digital converter (SAR ADC) stages. In aparticular embodiment, the invention includes a 3.2 μW WRX withsimplified 802.15.4g medium access control/physical layer (MAC/PHY)baseband, received signal strength indicator (RSSI) and clear channelassessment (CCA), forward error correction (FEC), and a cryptographicchecksum for industrial IoT applications. The charge-domain AFE providesa conversion gain of 26 dB with no static bias currents used anywhere inthe rectifier, CTSA, or SAR ADC. This provides robustness to process,voltage and temperature (PVT) variation, and pulsed interferencerejection.

Embodiments combine an ADC, a FIR filter and digital baseband to make awakeup radio. A FIR filter can be implemented by changing the CT valueovertime as the filter coefficient and summing with previous ADCsamples. ASK modulation and Manchester encoding is supported. On-offkeying (OOK) is a subset of ASK modulation. With the ADC, the WRX isable to support additional information encoded in the ASK RF message.Manchester is also supported. Multiple carrier frequencies aresupported. Aa an example, 100 MHz to 3 GHz is used for a practicalperformance. However, embodiments are capable of frequencies as low as˜10 MHz and as high as 100 GHz depending on the quality factor ofmatching network 302.

FIG. 1 is an illustration of a die layout (also referred to here asintegrated circuit (IC)) 101 including circuit components of a ULPreceiver according to an embodiment. The die includes an integrated CTSAand ADC 104, a clock generation circuit (CLKGEN) 106, and an RFrectifier circuit 108. As will be described in further detail below,embodiments of the invention provide improvements by colocatingcapacitors of the CTSA with those of the ADC in the circuit 104.

FIG. 1A is an illustration of a sensor node 110, according to anembodiment. The sensor node 110 has a form factor of approximately 5×5×8cm³. In this illustration, an antenna 112 is shown before the node unitis sealed. The IC 101 is present on the sensor node 110.

FIG. 2 is a system block diagram of a ULP receiver system. The systemincludes a Communication transceiver (Comm TRX) 202], a radio frequencyswitch (RF SW) 204, the antenna 112, energy harvesting input sources(EH-Sources) 208, and on-board sensors. A system-on-a-chip (SOC) 212includes a microprocessor (MCU) 204, energy harvesting power managementunit (EH-PMU) 206, CLK (or CLKGEN) 106, and WRX (also referred to hereinas wakeup receiver or ULP receiver) 300.

FIG. 3 is a block diagram of WRX circuit 300, according to anembodiment. In an embodiment, the WRX 300 is a fully-integrated sub-GHzWRX with charge-domain analog front-end in 65 nm CMOS. WRX 300incorporates a simplified 802.15.4g MAC/PHY baseband, RSSI and clearchannel assessment, forward error correction, and a cryptographicchecksum. It achieves a sensitivity of −67.5 dBm, SIR of −15.3 dB, RSSIaccuracy of ±3 dB, and power of 3.2 μW across PVT variation.

The WRX 300 is fully integrated into a system-on-a-chip (SoC) designedfor an energy-harvesting industrial IoT leaf node, but is suitable forany type of node. A leaf node is typically an outer node in a sensornetwork. Signals from antenna 112 go through matching network 302. Amain RF path (Main) from the antenna 112 and a dummy path (Dummy) from abroadband load form a pseudo-differential signal that improvescommon-mode rejection. In an embodiment, a conventional FR-4 substrate(a known glass-reinforced epoxy laminate material for printed circuitboards) and on-board inductor and capacitor (LC) components are used forthe matching network 302 to the custom antenna 112.

The charge-domain AFE 310 comprises parallel RF rectifiers 108, acharge-transfer summation amplifier (CTSA) 104A, and a 10-bit SAR ADC104B. The AFE 310 processes signals in the discrete-time charge domainas opposed to the traditional continuous-time analog approach. No staticbias currents are required, providing low-power and robust operationover a wide range of conditions. In an embodiment, the WRX 300 downconverts a Manchester encoded on-off keying modulation (OOK) RF wakeupmessage to baseband and digitizes the signal for demodulation, whileproviding reliable and rapid in-band and out-of-band interferencerejection. The WRX 300 supports received signal strength indicator(RSSI) and CCA, used by the network layer for continuous trafficmonitoring and link quality measurement.

Baseband physical layer (BB PHY) 304 receives signals from the ADC 104Band outputs a fast wakeup signal 306 and a secure wakeup signal 308. Thenetwork can be configured for either fast wakeups of only a Sync Word orsecure wakeups with a full WRX beacon packet with cryptographic checksumthat includes a payload for data transfer without the need for ahigh-power receiver.

A CLKGEN circuit 106, as further described below, controls the operationof the WRX 300. WRX CLK signal originates from an on-chip clock sourceusing an on-board crystal reference.

FIGS. 4A, 4B and 4C illustrate an embodiment of a charge domain AFE310that features RF rectification, charge-transfer amplification, and SARADC conversion based on charge redistribution.

FIG. 4A is a diagram of an RF rectification circuit 108, according to anembodiment. In one embodiment, the RF rectification circuit 108 includesmultiple Dickson rectifier chains in parallel and down converts the RFinput signal to the rectifier cap C_(R) as static charge. A reset phase(controlled by reset signal rst) is used in every stage, making surethere is no intersymbol interference caused by residual charge on CR.This front-end therefore supports a wide dynamic range of input powerlevels (from sensitivity level up to 7 dBm) without automatic gaincontrol.

In contrast to current solutions, parallel paths (leading to RECT_P_1and RECT_P_2) achieve a high signal-to-noise ratio (SNR) and fastsettling time. Specifically, longer chains (as in current solutions)produce higher settling times. As shown in FIG. 4A, embodiments includemultiple (M) paths with (N) stages per path. e.g. 2×15, or 3×10. Thensumming the M outputs from the N paths yields the final baseband output.This will settle faster than long chains because each M path is short(only N stages), yet has a better SNR compared to that of single N×Mstages.

FIG. 4B is a diagram of a CTSA circuit 104B, according to an embodiment.The CTAA stage shares capacitors with ADC 104B, and performsdifferential discrete-time summation and amplification throughswitched-cap operation. CDAC_P and CDAC_N are reused by CTSA as C_(O).The gain of the stage is determined by the capacitance ratio betweenC_(T) and the ADC 104B C_(DAC). At the interface at the output of the Mpaths (from FIG. 4A) summation and gain occurs. This is done in thecharge domain for more robust operation. The CTA circuit 104Beffectively takes multiple input branches, and sums them to a singleoutput, to provide both summation and gain. The CTSA circuit 104B takesin M analog inputs, and weights and sums each input on the output in thecharge domain, understanding that the output cap of the charge domainamp is the sample cap of an ADC. First, two parallel rectifier chainsdown-convert the RF input signal onto C_(rect) as static charge. A resetphase in every stage prevents intersymbol interference caused byresidual charge on C_(rect) and enables a wide dynamic range of inputpower levels without AGC. The following CTSA stage takes in parallel RFrectifier outputs, reuses ADC input DACs as its output capacitor C_(O),and performs differential discrete-time summation and amplification by again of C_(T)/C_(DAC). The differential ADC samples from the CTSA outputat the end of every cycle and performs asynchronous SAR operation basedon charge-scaling C_(DAC).

No static bias is used in the circuit.

FIG. 4C is a diagram of a SAR ADC circuit 104B, according to anembodiment. Circuit 104B receives CTSA_N and CTSA_P from the previousstage 104A and performs A/D conversion to generate multiple bits ofDOUT, which is for digital baseband demodulation.

FIG. 5 is block diagram showing a clock generator block (CLKGEN) 106that supports the discrete-time charge domain operation. CLKGEN 106takes in the WRX clock signal and outputs S₁, S₂ and reset (RST) signalsusing logic gates, flip flops, and delay lines. The charge-domain AFE310 seamlessly integrates RF down-conversion, baseband amplification,and A/D conversion without requiring driving-buffers and level-shiftingcircuits at each interface, thus saving power. The charge-domaintopology is inherently robust against PVT variation because it isfirst-order bias and V_(th) independent.

FIG. 6 shows the timing and signal diagram of the AFE 310. Threeclocking phases are required in every cycle of charge-domain operation.During the reset phase, C_(T) is fully discharged, and CDAC is chargedto V_(cm). During the pre-charge phase, inputs are reset to V_(cm), andsource nodes of all the NFETs are charged to V_(cm)-V_(th_n), andV_(cm)+V_(th_p) for PFETs case. As a result, all the transistors serveas analog source followers in this phase. When in the amplify phase, theinputs connect to parallel rectifier outputs providing a delta V_(in)(w.r.t V_(cm)), and the switch controlled by S₂* is released, initiatingcharge redistribution between capacitors C_(T) and C_(DAC). Therefore,the rectifier output is gained up by C_(T)/C_(DAC) due to chargeconservation. The effective capacitance of C_(T) is tunable through adigitally controlled 6-bit capacitor bank, providing tunable gain in theAFE. Finally, the differential ADC samples from the CTA output at theend of every cycle and performs a 10-bit asynchronous SAR operationbased on charge-scaling CDAC.

In an embodiment, the WRX is fabricated in 65 nm CMOS and occupies 0.33mm². It shows the measured results from 15 parts at 6 temperature pointsbetween −40° C. to 85° C. without any trimming. All measurements arereported with the SoC on-chip switching regulators and clock. AcrossPVT, the WRX achieves a mean sensitivity of −70.2 dBm for fast wakeupand −67.5 dBm for secure wakeup under 10% of packet error rate (PER),enabling in-network range in deployed industrial environments of 250 m,non-line-of-sight. It also demonstrates the in-band selectivityperformance of the WRX under CW interference at −500 kHz offset. A meansignal-to-interference ratio (SIR) of −16.5 dB is measured for fastwakeup and −15.3 dB for secure wakeups. A −65 dB out-of-band SIR at1.485 GHz offset (2.4 GHz) is achieved with the additional help from anon-board LC matching network without a SAW filter. In-band selectivityunder AM-type interference of an OOK packet with the same bit rate isalso measured, showing an SIR of 0 dB at 0 Hz offset, demonstrating afast interference rejection capability. The WRX achieves an RSSIaccuracy within ±3 dB from −67 dBm to −43 dBm without calibration. Themeasured power for secure wakeup is shown in FIG. 5, with a mean acrossPVT of 3.2 μW. A false-alarm rate of less than 10⁻³ is measured for bothwakeup modes.

What is claimed is:
 1. A circuit for radio frequency (RF) signal tobaseband conversion, comprising: an RF rectifier circuit configured toreceive an RF signal, wherein the RF rectifier processes the received RFsignal as multiple signal paths M and with multiple stages N per path;an amplifier circuit configured to receive output from the RF rectifiercircuit and perform summation and amplification operations on thereceived output from the multiple signal paths M; and ananalog-to-digital (ADC) circuit configured to receive an output of theamplifier circuit, and to convert the received output to a digitalbaseband format.
 2. The circuit of claim 1, wherein the amplifiercircuit is a charge domain amplifier circuit and at least the summationoperation is performed in the charge domain.
 3. The circuit of claim 1,wherein the received RF signal comprises amplitude shift keying (ASK)modulation.
 4. The circuit of claim 1, wherein the received RF signalcomprises Manchester encoding.
 5. The circuit of claim 1, wherein thecircuit is configured to operate at multiple carrier frequencies.
 6. Thecircuit of claim 1, wherein the output of the circuit includesinformation regarding received signal strength.
 7. The circuit of claim1, wherein the ADC circuit is a successive approximationanalog-to-digital (SAR ADC) circuit.
 8. The circuit of claim 1, whereinthe circuit does not include any static bias circuitry.
 9. The circuitof claim 1, wherein the amplifier circuit is further configured toreceive output from the RF rectifier circuit and perform a differencingoperation on the received output
 10. A charge domain amplifiercomprising: circuitry for receiving multiple input branches; circuitryfor summing the multiple input branches to a single output; andcircuitry for providing both summation and amplification in the timedomain.
 11. The amplifier of claim 10, further comprising circuitry forweighting and summing each input to be reflected on the single output inthe time domain.
 12. The amplifier of claim 10, wherein digitalinformation is stored as sampled charge on capacitors obtained from aradio frequency (RF) source, and wherein an output of the amplifiercomprises a sample capacitor of an analog-to-digital converter (ADC).13. The amplifier of claim 10, wherein the amplifier does not includeany static bias circuitry.
 14. A method for receiving and processingradio frequency (RF) signals, the method comprising: deploying a circuitfor radio frequency (RF) signal to baseband conversion, wherein thecircuit comprises. an RF rectifier circuit configured to receive an RFsignal; and an amplifier circuit configured to receive output from theRF rectifier circuit, wherein the method comprises; the circuitprocessing the received RF signal as multiple, parallel input signalpaths using the RF rectification circuit; the circuit performingsummation and amplification operations on the output of therectification circuit in the time domain using the amplifier circuit;and. the circuit generating a signal to an analog-to-digital converter(AI)C circuits) from the amplifier circuit, wherein the ADC converts thereceived signal from the amplifier circuit to a digital baseband format.15. The method of claim 14, wherein the amplifier circuit is a chargedomain amplifier circuit and at least the summation operation isperformed in the charge domain.
 16. The method of claim 14, wherein thereceived RF signal comprises amplitude shift keying (ASK) modulation.17. The method 14, wherein the received RF signal comprises Manchesterencoding.
 18. The method of claim 14, wherein the circuit is configuredto operate at multiple carrier frequencies.
 19. The method of claim 4,wherein the output of the circuit includes information regardingreceived signal strength.
 20. The method of claim 14 wherein the ADCcircuit is a successive approximation analog-to-digital (SAR ADC)circuit.
 21. The method of claim 14, wherein the circuit does notinclude any static bias circuitry.
 22. The method of claim 14, whereinthe amplifier circuit is further configured to receive output from theRF rectifier circuit and perform a differencing operation on thereceived output.